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Distributor Advance

vette

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With the distributor on the bench is there a practical way to tell how far a given distributor will advance? Thanks.
 

gonzo

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Hummm. Are max degree advancement stamped on the distributor weights or their springs color coded to indicate degree of advancement.
 

red57

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I think it would take a distributor machine but since everything is computer controlled these days, finding a shop that has one (and someone who knows how to operate it) may be tough. A quick eBay search showed a few old Mallory, Sun, etc. between $600 and $2500. You might get lucky if there are any old engine/machine shops in your area.
 
OP
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Thanks for the replies guys. Gonzo has spoken the truth in some cases but not always. Truth be known this isn’t for the Healey. It’s an aftermarket dizzy for my old Vette with a 383 in it. To be totally transparent i asked the question here because I know the people here respond with some seriousness. That’s not always the case on some other forums.
So having said all that here’s the problem.
I bought this dizzy to replace a very worn original. But I can only get about 24 degrees of total advance out of it. I’ve tried a variety of springs and weights but I always end up with 24* total. Many of these dizzys have a pin in a slot that stops total advance. Sometimes this pin has a bushing on it which’s limits the rotation of the plate. This one does not which means I don’t understand why I’m not getting full advance. I have a Crane module in the car which has been in use even with the old dizzy but I’m starting to wonder if it could be in the module. But all my test and checks I’d like to be able to know on the bench how far the plate is advancing. I’m thinking I could lay out degrees but I think it would be hard to be accurate. I’m sorry this isn’t about a Healey but hey what can I say… I trust you guys.
 

John Turney

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Can you put a mark on the inside of the housing that lines up with something on the movable plate and rotate the plate by hand until it stops. You should be able to use pi*(d/2) to figure out the degrees.
 
OP
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Can you put a mark on the inside of the housing that lines up with something on the movable plate and rotate the plate by hand until it stops. You should be able to use pi*(d/2) to figure out the degrees.
John, thank you for the help. I took the formula, substituted "x" for the asterisk and solved for "x". I will admit that I am rusty on my ritmetic but in transposing the formula here is what I came up with. (Pi) (x) (d/2) = 1
1 / (Pi) (d/2) = x If I imagine a 4" circle just for discussion,
1/ (3.14) 2 = x
1/ 6.28 = x
.1592 inches = x So, .1592" = 1 degree of rotation. And .1592" is almost 1/6 of an inch.
Seems to me that .1592" is going to be hard to measure. But if my calculation is correct it does give me a second checking method.
Did I get the ritmetic right? Thank you for your help.
 

PHulst

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Thanks for the replies guys. Gonzo has spoken the truth in some cases but not always. Truth be known this isn’t for the Healey. It’s an aftermarket dizzy for my old Vette with a 383 in it. To be totally transparent i asked the question here because I know the people here respond with some seriousness. That’s not always the case on some other forums.
So having said all that here’s the problem.
I bought this dizzy to replace a very worn original. But I can only get about 24 degrees of total advance out of it. I’ve tried a variety of springs and weights but I always end up with 24* total. Many of these dizzys have a pin in a slot that stops total advance. Sometimes this pin has a bushing on it which’s limits the rotation of the plate. This one does not which means I don’t understand why I’m not getting full advance. I have a Crane module in the car which has been in use even with the old dizzy but I’m starting to wonder if it could be in the module. But all my test and checks I’d like to be able to know on the bench how far the plate is advancing. I’m thinking I could lay out degrees but I think it would be hard to be accurate. I’m sorry this isn’t about a Healey but hey what can I say… I trust you guys.
Mallory?

There is a distributor rebuilder in Illinois who can rebuild your stock distributor to better than new. He has done a couple Corvette ones for me, and I have one from a '63 convertible that I need to send him.
Unfortunately he's in FL for the winter, but I'd have him redo your original long before I'd go with the aftermarket.
 
OP
vette

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There is a distributor rebuilder in Illinois who can rebuild your stock distributor to better than new.
Thanks PHurst, but that’s no fun.
I'd have him redo your original long before I'd go with the aftermarket.
The aftermarket one is a rebuilt original. I should have just rebuilt it myself but I was feeling lazy. I’ll just have to strip this one to parade rest and start from scratch. I’ll probably make a degree wheel to see how far the plate moves. Thanks again.
 

PHulst

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The problem is that you have no idea what advance cam, springs and weights are on the “rebuilt” one.

Your best bet is to find someone with a distributor machine, and check them both out.
 
OP
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Just a fun little project. I have a drawer full of weights and springs most are tagged according to what engine I took them from. I have the original weights and springs from the Vettes original 350 cu. in engine. I won't have any trouble deciding what weights and springs to use. Over the years myself and many friends have built and tuned engines. Many time we would interchange weights and springs to see if we could get a better advance rate and curve that would improve performance. Sometimes we would end up with two different springs and two different weights, sometimes we would end up with the originals. It all depended on what we were trying to achieve. I have even filed weight off of weights to achieve an advance profile I wanted and many times have polished weights to get them to respond quicker. But aside from putting it back into the car to see what it will do after a certain modification right now all I want to do is to see if the base plate is actually moving as far as it should go without any weight or springs attached. I want to know what degrees that is. You might remember from the origin question I wanted to decipher how far in degrees the advance plate was moving, ON THE BENCH.
 

John Turney

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John, thank you for the help. I took the formula, substituted "x" for the asterisk and solved for "x". I will admit that I am rusty on my ritmetic but in transposing the formula here is what I came up with. (Pi) (x) (d/2) = 1
1 / (Pi) (d/2) = x If I imagine a 4" circle just for discussion,
1/ (3.14) 2 = x
1/ 6.28 = x
.1592 inches = x So, .1592" = 1 degree of rotation. And .1592" is almost 1/6 of an inch.
Seems to me that .1592" is going to be hard to measure. But if my calculation is correct it does give me a second checking method.
Did I get the ritmetic right? Thank you for your help.
The "*" is a times sign on a keyboard. With a 4" diameter distributor, the circumference of the distributor would be pi*4"/2 = 3.14159 * 4/2 = 6.2832". Divide that by 360 to get 0.0175" per degree. 25 degrees is 0.4363", about 14/32" or 7/16".
 
OP
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Hey John that's great. I can use that. Thank-you.
Dave.
 

Joe Schlosser

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Circumference of a circle is PI X D. NOT D/2. The area of a circle uses the radius or D/2
4" diameter has circumference of 12.56 inch.
one degree is 0.034 inch. 25 degrees is 0.87 inch
 
OP
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Thanks guys for all your help.
 
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